title: Metastases to the liver from neuroendocrine tumors: effect of duration of scan acquisition on CT perfusion values.
abstract: OBJECTIVE
  To assess the effects of acquisition duration on computed tomographic (CT) perfusion parameter values in neuroendocrine liver metastases and normal liver tissue.
  
  
  METHODS
  This retrospective study was institutional review board approved, with waiver of informed consent. CT perfusion studies in 16 patients (median age, 57.5 years; range, 42.0-69.7 years), including six men (median, 54.1 years; range, 42.0-69.7), and 10 women (median, 59.3 years; range 43.6-66.3), with neuroendocrine liver metastases were analyzed by means of distributed parametric modeling to determine tissue blood flow, blood volume, mean transit time, permeability, and hepatic arterial fraction for tumors and normal liver tissue. Analyses were undertaken with acquisition time of 12-590 seconds. Nonparameteric regression analyses were used to evaluate the functional relationships between CT perfusion parameters and acquisition duration. Evidence for time invariance was evaluated for each parameter at multiple time points by inferring the fitted derivative to assess its proximity to zero as a function of acquisition time by using equivalence tests with three levels of confidence (20%, 70%, and 90%).
  
  
  RESULTS
  CT perfusion parameter values varied, approaching stable values with increasing acquisition duration. Acquisition duration greater than 160 seconds was required to obtain at least low confidence stability in any of the CT perfusion parameters. At 160 seconds of acquisition, all five CT perfusion parameters stabilized with low confidence in tumor and normal tissues, with the exception of hepatic arterial fraction in tumors. After 220 seconds of acquisition, there was stabilization with moderate confidence for blood flow, blood volume, and hepatic arterial fraction in tumors and normal tissue, and for mean transit time in tumors; however, permeability values did not satisfy the moderate stabilization criteria in both tumors and normal tissue until 360 seconds of acquisition. Blood flow, mean transit time, permeability, and hepatic arterial fraction were significantly different between tumor and normal tissue at 360 seconds (P < .001).
  
  
  CONCLUSIONS
  CT perfusion parameter values are affected by acquisition duration and approach progressively stable values with increasing acquisition times. Online supplemental material is available for this article.
authors.affiliation: From the Departments of Diagnostic Radiology (C.S.N., E.F.A., D.H.H., C.C.), Biostatistics (B.P.H.), Imaging Physics (A.G.C.), and Gastrointestinal Medical Oncology (J.Y.), The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1473, Houston, TX 77030-4009.
authors.forename: Chaan S
authors.initials: CS
authors.lastname: Ng
authors.forename: Brian P
authors.initials: BP
authors.lastname: Hobbs
authors.forename: Adam G
authors.initials: AG
authors.lastname: Chandler
authors.forename: Ella F
authors.initials: EF
authors.lastname: Anderson
authors.forename: Delise H
authors.initials: DH
authors.lastname: Herron
authors.forename: Chusilp
authors.initials: C
authors.lastname: Charnsangavej
authors.forename: James
authors.initials: J
authors.lastname: Yao
mesh_terms: D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D001810:Blood Volume; D005260:Female; D006499:Hepatic Artery / Q000000981:diagnostic imaging; D006801:Humans; D008099:Liver / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000473:pathology; D008113:Liver Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000556:secondary*; D008297:Male; D008875:Middle Aged; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging*; D018358:Neuroendocrine Tumors / Q000473:pathology*; D012189:Retrospective Studies; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*